Conventionally, various fuel injection control devices for internal combustion engines have been designed. For example, in Japanese Patent Laid Open Publication Number 59-176427, a fuel injection control device has been developed to control a fuel injection quantity according to an intake air temperature. The fuel injection quantity is corrected, so as to compensate for a difference in density of the intake air due to a temperature difference thereof. The correction value of the fuel injection quantity according to the intake air temperature is determined based upon an output signal from an intake air temperature sensor provided in an air cleaner, for example. While idling or running with a very low load with respect to the internal combustion engine, the intake air flow is relatively small, and thus, the temperature of a temperature detecting portion of the intake air temperature sensor accurately corresponds with the actual intake air temperature.
On the other hand, when the engine becomes hot as in a high load condition, the temperature of the temperature detecting portion of the intake air temperature sensor can read a very high temperature due to the influence of the high ambient temperature around the sensor even though the actual intake air temperature is not as high due to the large intake air flow. More specifically, when an intake air temperature is detected by the intake air temperature sensor during a high load condition, the detected intake air temperature is actually higher than the actual intake air temperature.
As a result, if the corrected value of the fuel injection quantity is determined based upon the detected intake air temperature only, a problem exists such that the fuel injection quantity according to the detected intake air temperature during a high load condition is different from a fuel injection quantity which would be corrected on demand by the engine if the actual intake air temperature was detected.
Another example of a fuel injection control device for an internal combustion engine is set forth in Japanese Patent Publication Number 63-14173. This fuel injection control device improves in acceleration performance by increasing a fuel injection quantity during acceleration of an internal combustion engine. This technique utilizes a threshold value for determining acceleration that is variable according to engine temperature. The fuel injection quantity is increased according to the determination of the acceleration.
In contrast, another technique for adjusting the acceleration incremental injection quantity according to an engine temperature utilizes a water temperature correction factor. In this technique, a fuel injection quantity, during normal running of an engine, is usually corrected by utilizing a water temperature correction factor set according to an engine temperature. The acceleration incremental injection quantity is corrected utilizing this water temperature correction factor.
However, utilizing such a correction technique, the fuel injection quantity for normal running of an internal combustion engine and the acceleration incremental injection quantity are corrected utilizing the same water temperature correction factor. In other words, the temperature correction factor used during normal running of an internal combustion engine is used during acceleration or transient running of the engine. Accordingly, this type of correction technique is not desirable in a motorcycle in which acceleration performance is considered an important feature. More specifically, when utilizing this correction technique, the fuel injection quantity which is computed utilizing the correction factors stated above, it is quite different from the actual fuel injection quantity demanded by the engine.